I have a 2005 500, there is no cabin filter. Normally it would be behind the glove box but a decision was made somewhere not to install one or even complete the opening. Go to http://www.fordtaurus.net/forums/viewtopic.php?f=5&t=10615 and you can find out how to make the opening and what type of filter to use.

Who's 'they'? How was the charge level verified? Some after-market cabin filters come with instructions , and if you get it at a dealer ,they might be able to give you a print-out of the parts break-down , which may be helpful.